Google and Facebook are "making money hand over fist" and it’s time they use some of that cash to sort the problem of ad fraud by a fixed date, according to The&Partnership founder and chief executive Johnny Hornby.

Hornby – whose agency is part of the WPP group and who has been long-tipped as a potential successor to Sir Martin Sorrell – echoed the sentiments of his boss when he said enough was enough when it comes to Google and Facebook paying lip service to the issue of fraud.

"They need to act quickly, like now, and make a promise to invest a proper amount of money against a deadline. We need to say that we won’t sit on another panel in Cannes and have this same discussion," he said at the Guardian Media Summit, referring to the global advertising event that takes place in June.

"These are not organisations that don’t have the money to put software in place. They have software that allows them to take money from advertisers and put videos on Jihadi sites. Use the same money to stop it. They have the financial might to do a lot more about this than simply going to conferences and recognising these are issues."

Digital advertising expenditure is expected to rise to $80bn this year, and Facebook and Google will together take more than 70% of that spend.

Hornby went on to suggest that WPP should partner with other groups, media companies and trade bodies and threaten to stop spending any money with Facebook and Google "unless you sort this out by the end of Cannes."

"That’s the sort of thing that should happen or we’ll all be sitting talking about it in another year with another $16bn lost," he added, referring to the figures the agency released on the potential loss advertisers face to ad fraud in 2017.

In the meantime, "clients need to stop asking agencies to buy cheap media, and agencies have to refuse to do that," he warned.

Google, for its part, announced an independent audit of YouTube’s ad metrics soon after a scathing expose by The Times into ad fraud and an equally cutting speech by P&G's top marketer Marc Pritchard. However, the online behemoth's new UK managing director, Ronan Harris has insisted that improving transparency isn't down to just one company.

"The conversation needs to be about the standard we want to set ourselves as an industry," said Harris.

"I want to listen to the concerns: I want to hear them and I want to talk about what we’re doing and discuss whether there are things we can do better."

"We’re one player in an industry of 1,000 and I want to be clear about the standards that we collectively set for ourselves and that we all drive toward them. If I can be a catalyst in that conversation, then I’m happy to do so both in my role as UK managing director but also in a personal capacity."

But, for all of Hornby’s talk of potentially pulling ad spend if resolutions aren’t found, it’s clients that will have the final say on the where budgets go and from the few that spoke at the Guardian's conference, digital pounds seem to only be going one way.

TUI’s general manager for digital marketing Christian Armond accepted that it’s impossible to cut ad fraud out completely and it’s simply trying to mitigate risk. Currently, fraud for the brand is a "3% to 5% problem, not 30% to 50%."

"This could be because we’re doing what we need to be doing, that there are unknown unknowns or if it’s the scare tactics that drive you towards these sorts of solutions. We have a responsibility to take control of ownership, and implement the tools to be able to measure that use of the data and see where our ads are appearing," he said.

On a separate panel on the challenge of measurement in the walled gardens of Facebook and Google, Mondelez's media manager for Northern Europe Derek Luddem, said that Facebook's admission that it had made a number of measurement errors had did little to dissuade him halting spend on the platform.

Elsewhere, Barnaby Dawe, global chief marketing officer at Just Eat revealed that it will double its spend on Facebook this year.